Peelable packaging films are frequently utilized in diverse container sealing applications. Primarily they are used to seal the mouths of foodstuff or medicine containers. In such applications, they provide closure of the mouth to prevent unintended loss of the contents. They also provide a solid, vapor, and liquid-tight barrier to prevent contamination and spoilage of the contents. In addition, being non-resealable once opened, they provide a security function by alerting the consumer whether the contents of a presumably unopened container have been potentially tampered with. Films intended for container sealing applications such as these are sometimes referred to as “lidding” films.
Conventional lidding films typically include at least two component layers. First, a base layer forms a mechanical closure preventing foreign substances from entering the container. Second, a seal layer which most commonly is thermally adhered to the circumference of the container mouth, provides a seal removable by peeling, preferably without tearing or leaving sealant material on the container. Many sophisticated modifications and additions to these basic components have developed to provide advantageous features to peelably lidded containers.
A particular disadvantage of many peelable-lidded containers is that the adhesion of the lidding film to the container is so strong that the film is difficult to remove from the container. Additionally, the strong adhesion can undesirably wholly or partially delaminate the lidding film leaving pieces of the film adhered to the lip of the container mouth. However, if the adhesion to the container mouth is made too weak, the lidding film can be removed inadvertently or prematurely by many incidental causes including, for example, pressure and movement of the contained material.
U.S. Pat. No. 6,616,998 and U.S. Pat. No. 5,888,599 disclose exemplary conventional peelable, sealable films used for lidding and packaging foods. These films are prepared using multi-step processes in which a core film is first prepared. This core film forms a base layer that is then coated with a hot melt adhesive in a separate step to form a skin layer, whose function is to provide a peelable heat seal.
In addition, other sealable films known in the art are coextruded. While these coextruded films are cost-effective to produce, the obtained films are not truly peelable as they often tear and split when removed from the package, often sticking to the food, especially to foods that contain sauces and cheese such as pizza.
A desirable beneficial feature of lidding films is inclusion of a highly effective moisture and/or gas barrier layer. Preparation of lidding films having thin barrier layers and desirable adhesive characteristics is usually difficult. It is particularly desirable to provide a multilayer lidding film having an organic barrier layer, which can be heat sealed to the mouth of diverse container compositions with a proper balance of adhesive characteristics. That is, the lidding film should bond firmly and durably to the container, be removable with moderate peeling force by the consumer and substantially completely peel from the container intact such that no lidding film residue is retained on the opened container.